Meteorological observation data such as temperature, humidity, wind speed and wind direction are important for
validating and improving numerical weather simulation models. Lidar is an effective method for acquiring such data
with high range resolution and short time intervals. In this study, we carried out a field observation with coherent
Doppler Lidar and Raman Lidar systems at the coastal area of Yokosuka, Japan, and compared the observed data with
the results of numerical weather simulations. We obtained the vertical profiles of horizontal wind speeds and wind
directions by Doppler Lidar with 65 m vertical range resolution, and the vertical profiles of the water vapor mixing ratio
by Raman Lidar with 20 m vertical range resolution at the lower atmospheric boundary layer (200-600 m height from
ground level). These data were acquired at time intervals of 10 minutes. We found an interesting phenomenon from
observed data indicating that, under weak wind conditions, water vapor in the atmosphere significantly increased just
after a definite change in wind direction from land breeze to sea breeze. A similar phenomenon was also predicted by the
numerical weather simulation with the same meteorological and terrestrial conditions. We analyzed the numerical results
and found that the change in water vapor mentioned above is mainly caused by the difference between the evaporation
from land and sea surfaces, which were located upwind of the land and sea breezes, respectively.
Hydrogen is expected to become an energy source in the next generation. Although hydrogen gas is a combustible gas
with a large explosion concentration range, leakage is presently monitored by contact type gas sensors. The technology
for locating a leak and remote sensing of gas concentration distribution is required in case of hydrogen gas leaks. In this
study, remote sensing technology of hydrogen gas concentration distribution using a Raman lidar was developed. The
lidar system consisted of a pulsed Nd:YAG laser of wavelength 354.7 nm and a Galilean telescope of aperture 170 mm.
The system could detect hydrogen gas by vibrational Raman scattering. In this method, hydrogen gas concentration
could be measured based on the ratio of the Raman scattering signals from hydrogen gas and from atmospheric nitrogen,
which were simultaneously measured. In this manner, the geometrical form factor of the biaxial lidar and the
instrumental function were canceled. Hydrogen gas concentration of 0.6-100% could be measured at a distance 13m
using this system.
Raman lidar is commonly used for measurement of water vapor profiles in the lower atmosphere. However, the
treatment of the Raman lidar signals from clouds is not well established. A simplified model taking multiple scattering
into account is proposed. The model results in a difference of two exponential functions, one which represents the
extinction of laser light inside the cloud, and another which represents the effect of multiple scattering. The model was
applied to measurement results using a Raman lidar system consisting of a laser wavelength of 280 nm and detection
channels for Raman scattering from water vapor and atmospheric nitrogen. When a cloud was present in the field of view
of the lidar, the water vapor Raman scattering signal increased from almost zero at the cloud base to a maximum at a
penetration distance of about 50 m, whereas the nitrogen Raman scattering signal decreased monotonously beyond the
cloud base. This behavior could be explained by the model, and the measured signals could be adequately reproduced by
setting the decay constant of one exponential function equal to the attenuation coefficient of the nitrogen Raman
scattering signal, and optimizing the decay constant of the other exponential function. Comparison of measurement
results and calculation results based on the model showed that the model is mainly applicable to optically thick clouds,
for which the attenuation coefficient is larger than 0.02 m-1.
Lidar is a powerful remote sensing tool to monitor the weather changes and the environmental issues. This technique
should not been restricted in those fields. In this study, the authors aim to be apply it to the prediction of weather
disaster. The heavy rain and the lightning strike are our targets. The inline typed MPL (micro pulse lidar) has been
accomplished to grasp the interaction between the low altitude cloud and the atmosphere and to predict the heavy rain,
while it was hard to catch the sign of lightning strike. The authors introduced a new algorism to catch the direct sign of
the lightning strike. Faraday effect is caused by lightning discharge in the ionized atmosphere. This effect interacts with
the polarization of the propagating beam, that is, the polarization plane is rotated by the effect. In this study, high
precision polarization lidar was developed to grasp the small rotation angle of the polarization of the propagating beam.
In this report, the interaction between the low altitude cloud and the atmosphere was monitored by the high precision
polarization lidar. And the observation result of the lightning discharge were analyzed.
Prediction of weather disaster such as heavy rain and light strike is an earnest desire. Successive monitoring of the low altitude atmosphere is important to predict it.
In this study, high precision polarization lidar was developed to observe the low altitude atmosphere. This lidar has the high extinction ratio of polarization of >30dB to detect the small polarization change of the atmosphere. The change of the polarization in the atmosphere leads to the detection of the depolarization effect and the Faraday effect, which are caused by ice-crystals and lightning discharge, respectively. The long-term observation was accomplished at low elevation angle. It aims to monitor the low altitude atmosphere under the cloud base and capture its spatial distribution and convection process. The observation has been continued in the cloudy and rainy days. The thunder cloud is also a target.
An in-line typed new concept lidar system for high precision polarization measurement was
developed. A specially designed polarization-independent optical circulator, which was composed
by Gran laser prisms and highly transparent Faraday rotators, was developed. Its isolation
between the orthogonal polarizations was improved up to more than 30 dB. It is sufficient to
detect small rotation of the polarization plane of the propagating beam caused by lightning
discharges due to the Faraday effect. The rotation angle of the polarization plane is estimated by
the differential detection between the orthogonal polarization components of the lidar echoes. The
in-line optics enables near range measurement from the near range of >30 m with the narrow field
of view of 0.17 mrad. The fundamental measurements of lidar echoes in near and far fields, and
low cloud activities were examined.
A Raman lidar system for detection of hydrogen gas has been developed. The lidar system consists of a pulsed Nd:YAG laser of wavelength 355 nm and a Newtonian telescope of aperture 212 mm. The system can detect hydrogen gas by either rotational or vibrational Raman backscatter up to a distance of 30 m in outdoor, daylight conditions. Furthermore, the system can perform two-dimensional mapping of the hydrogen gas distribution by spatial scanning of the laser beam within the telescope field of view.
This study examines the feasibility of optical remote measurement of the electromagnetic field or the electron density
distribution in thundercloud. We considered the contribution of Faraday effect as the magneto-optical effect to the change
in polarization of the backscattered light, assuming a polarizing lidar configuration. We estimate that, if the lidar can
detect the polarizing rotation angle in the plane perpendicular to the propagating beam with a dynamic range of more
than 30dB, the lidar can be used to predict lightning strikes.
An acousto-optic laser deflector was used to obtain shadowgraphs and laser interference fringe patterns at microsecond-order exposure times by blocking the undeflected light and exposing the imaging device to the deflected light. This method allows μ-order imaging using an ordinary CCD camera, and is less susceptible to damage resulting from incidence of high intensity light, which is a problem when using image intensifiers. Using this method, shadowgraphs and laser interference fringe patterns showing density changes accompanying spark discharges in air, pre-breakdown phenomena such as streamers and leaders, and laser-induced breakdown in air were obtained. In addition, by sequentially applying high frequency signals of different frequencies, the incident light was deflected to different regions of the CCD chip, which allowed time-resolved imaging of laser interference fringes.
Hydrogen flame, which emits only in the ultraviolet and infrared regions and is therefore invisible, was visualized by imaging at 309 nm, which corresponds to the peak in the OH emission. The background was imaged simultaneously at 337 nm, where the flame emission is very weak. Both images were obtained using narrowband interference filters of 1.5 nm bandwidth and image intensifiers, and the flame image was extracted from the difference in the intensity of the images at the two wavelengths. A combination of (1) digitization using a threshold intensity level and (2) Gaussian blur were applied to the difference image for rejection of spurious spots which resulted from the grainy appearance of the image obtained by the image intensifier. This method allowed elimination of reflected sunlight. The method was also used to image hydrogen flame using interference filters of 10 nm bandwidth. The flame region was successfully extracted up to a working distance of 30 m under outdoor daylight conditions.
We performed SO2, NO2, and 03 measurements in the lower troposphere using a multiwavelength differential absorption lidar (MDIAL) system. Measurement results are compared with results of airborne and ground-based in-situ measurements performed simultaneously with lidar measurement. Vertical concentration variation of SO2 with 0-7 ppb for 1000-1700 m altitude was measured by dual-DIAL, and those ofNO2 and 03 with 0-50 ppb for 700-2000 m altitude were measured by 2-wavelength DIAL quasi-simultaneously. Measurement results suggest that NO2 was trapped below the inversion layer, which induced the reduction of 03 concentration by the reaction with NOR. Comparison of results obtained by DIAL and by in-situ methods showed that the MDIAL system had sufficient accuracy for verification of long-range transport models of sulfur compounds and for observation of chemical reactions of oxidants and nitrogen oxides. We also performed simultaneous profiling of NO2 and 03 in the lower troposphere using a stable, high power transmitter for NO2 measurement. Concentration variations ofNO2 and 03 for 900-1350 m altitude were measured for a continuous time interval of 24 hours without maintenance.
A lidar system capable of simultaneous measurement of Raman and Mie-Rayleigh scattering was constructed, and used for measurement of 03, water vapor, and aerosols in the lower troposphere. 03 concentration measurement was performed by differential absorption of N2 and 02 Raman scattering signals with the lidar transmitter operating at 280.0 nm, and also by differential absorption of Mie-Rayleigh scattering and of N2 Raman scattering with the transmitter operating at 279.5 nm and 280.5 nm on alternate pWses. Water vapor profiles were obtained as the mix ing ratio relative to N2 using the N2 and H20 Raman scattering signals with the lidar transmitter operating at 280.0 nm. Simultaneous measurement of H20 Raman scattering and Mie scattering over a continuous period of about 13 hours showed that the lidar system can identify uncondensed water vapor and condensed water vapor by comparison of temporal and spatial variations of the water vapor mixing ratio and of the Mie backscattering coefficient.
Vertical concentration profiles of O3 and NO2 in the lower troposphere were measured simultaneously using a multi wavelength differential absorption lidar (DIAL) system based on a pair of Nd:YAG pumped dye lasers each capable of emitting two wavelength on alternate pulses. A mixture of Rhodamine 590 and Rhodamine 610 dyes and second harmonic generation was used to generate wavelengths 288.2 nm and 293. 5 nm for O3 measurement, and sum frequency mixing of LDS765 dye laser radiation with Nd:YAG fundamental was used to generate wavelengths 448.1 nm and 446.8 nm for NO2 measurement. O3 profiles of approximately 30-50 ppb and NO2 profiles of 0-20 ppb were obtained for vertical range 1500-2500 m. The measurement error was estimated to be < 6 ppb for 150 m range resolution, or < 0.9 ppm-m, for both O3 and NO2.
A multiwavelength differential absorption lidar (DIAL) system for measurement of trace atmospheric substances was developed. Vertical concentration profiles of SO2 in the lower troposphere were measured by three wavelength dual-DIAL (on wavelength=300.05 nm, off wavelengths=299.35 nm, 300.90 nm, with null profiles obtained at 300.05 nm) . The measurement wavelengths were chosen to minimize the effect of O3 . Measurement results showed an average SO2 concentration of 0.6 ppb for height 2000-4000 m, and the SO2 measurement error was estimated to be about 1 ppb for 150 m range resolution. Although the measured SO2 concentration was below the resolution of our system, the results show that the system is capable of measuring trace SO2 with approximately 0.15 ppm-m resolution. In addition, vertical O3 concentration profiles in the lower troposphere were measured using two identical DIAL pairs (on wavelength=285.0 nm, off wavelength=290.1 nm), from which two null profiles and two DIAL profiles were obtained simultaneously. The DIAL profiles, which showed an average O3 concentration of 42 ppb for height 1000-4000 m, agree with simultaneous O3 sonde measurements. The effect of backscatter gradients was shown to be small. The O3 measurement error was estimated to be 3.4 ppb for 150 m range resolution, or about 0.5 ppm-m.
Vertical NO2 concentration profiles, which are important in studies of atmospheric chemistry and urban pollution, were measured by a differential absorption lidar (DIAL) based on a pair ofNd: YAG pumped dye lasers. In the experiment, 448.1 nm and 446.8 am were used for the "on "and "off' wavelengths, respectively. NO2 concentration profiles of 0-40 ppb were obtained for altitude 900 —2250 m with 150 m range resolution. Null error, which was estimated by the deviation ofthe null profile from zero, was <2ppb. The statistical error, systematic error from aerosols, and error due to uncertainty of absorbtion cross section were ?3.35 ppb, <3 ppb and <1 ppb, respectively. The total error was about 5 ppb. The estimation of aerosol backscatter and extinction error in NO2 measurement due to inhomogeneous aerosol distribution is treated in detail.
We show that the coordinate-transformed mode which is the transformation from a Gaussian profile to a uniform circular one inside a cavity, is selected through iteration of round trips, using Fox-Li simulation in a bare cavity. When the phase constraint due to cavity mirrors is predominant, the intensity profiles converge to the desired profiles.
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